Lava is red hot when it pours or blasts out of a vent but it usually changes to dark red, black or grey as it cools and solidifies. Although volcanoes can be destructive, they can be constructive too. Over 80 percent of the Earth's surface (both above and below sea level)
originally came from volcanoes. And the gasses sent out from volcanic vents - which are mostly water vapor - formed the Earth's earliest oceans and atmospheres.
What does active, dormant and extinct mean? Mount Etna, 1985
Active volcanoes are simply volcanoes which have erupted recently or still have a chance of erupting. Dormant is if a volcano has not erupted for a long time but still has signs of future eruptions. It is when a volcano has hardened lava clogged up in the vent/vents. They are usually very violent if they erupt again because of the immense pressure of magma building up. Once they have erupted again they are classified as active volcanoes. Extinct volcanoes are those which have not erupted for tho usands of years. It is hard to tell if a volcano is dormant or extinct. They have to be listed as dormant until it is certain that there will be no more eruptions.
The picture on the right shows Mount Etna, an active volcano in Sicily, Italy
Mauna Kea, 1971
The picture on the left shows Mauna Kea, a dormant volcano in Hawaii.
Mount Kilimanjaro
On the right is Mount Kilimanjaro in Tanzania, Africa
Where are volcanoes found?
Volcanoes are found at plate boundaries. It happens when plates clash together, pull away from each other or slide together. Most are on land and some are underwater.
The Pacific ring of fire
This Pacific Ring of Fire is an arc stretching from New Zealand along the eastern edge of Asia, north across the Aleutian Islands of Alaska, and south along the coast of North and South America. It is located at the border of the Pacific Plate and other tectonic plates.
Volcanic eruptions are caused when two plates have or break contact with one another. Always resulting with exposure of magma.
Diagram of a typical volcano
Composite volcanoes
Composite volcanoes are another name for strato volcanoes. They are made by alternating layers of lava flows, volcanic ash, cinders, blocks, and bombs. They can rise up to 8000 feet above there bases. Some of the most beautiful mountains in the world are composite volcanoes including in Japan, in Ecuador, in California, in Oregon, and in Washington.
Composite volcanoes are usually explosive, this is because of the ‘viscous’ magma. When the viscous magma rises to the surface, it usually clogs the crater pipe; the gas in the crater pipe gets stuck, causing immense pressure. This causes the volcano to erupt in an explosive way.
Strato volcanoes are built up while passing through subduction zones.
Shield volcanoes
Shield volcanoes are made almost entirely of flowing lava. As it pours and pours out of the vent again and again making the shape of the volcano flat and broad shaped which looks rather like warriors shield. They are formed when thousands and thousands of fluid basaltic rock in great distances. It becomes thinner as it cools. Some of the largest volcanoes in the world are shield volcanoes. In northern California and Oregon, many shield volcanoes have diameters of 3 or 4 miles and heights of 1,500 to 2,000 feet. The are made of rows of these volcanoes including Kilauea and Mauna Loa on the island of Hawaii - two of the world's most active volcanoes. The floor of the ocean is more than 15,000 feet deep at the bases of the islands. As Mauna Loa, the largest of the shield volcanoes (and also the world's largest active volcano), rises 13,677 feet above sea level, its top is over 28,000 feet above the deep ocean floor.
Living near Volcanoes
Many people live near volcanoes. This is a great risk to them as the volcano may easily erupt and kill them all. So why continue to live there? The answer is, volcanoes produce fertile soil, and provide valuable minerals, water reservoirs, geothermal resources, and scenic beauty. Also, most volcanoes are very infrequent – they erupt about once every thousands of years. Most people take the risk. They may have lived there for generations and just don’t want to move, some may just like the excitement of it all!
